TRANSMISSION PROBLEMS I THINK ????

Isuzu Other

I have a Isuzu trooper 02(automatic) 4x4(witch stop working) 3.5l engine 100,250 miles. Almost every time I give it gas or just let go off the brake it king of tugs. When it shifts to first or second gear (not really sure) at first it tugs but than it goes fine. If I warm it up for longer it happens less. One mechanic told that I need a new transmission and he wants $2500.00 for a used one.
I'm afraid that more I drive it the worse it's gonna get, but I only have that one car and have to drive it. Please help. THANK YOU! : D